The causes of breast cancer remain unknown. It has been observed that following chemotherapy certain white blood cell (called CD4+ T lymphocyte) levels are significantly reduced. These cells are very important in the response of the body to fight foreign agents such as bacteria, viruses and tumor cells. It has also been observed that no drugs can successfully increase this cell count. The mechanisms by which these white blood cells are increased in the body are not well understood. The investigators feel that some type of exercise therapy program may help to increase these cells. If exercise does help, then such therapy can be used to enhance the health of women. In this study, the investigators propose to determine the influence of exercise training and its impact on these white blood cell levels. In addition, we want to see how exercise effects functional abilities following chemotherapy. After preliminary testing, volunteers will be randomly assigned to one of two groups. Volunteers in the training group will go through a familiarization period prior to testing and training so that they know how to perform the tests and exercises.